Text-box width becomes really narrow when screen collapses

I have a text block where the paragraph has about 570px width. I want to keep that text width until the screen width is about 580px. Then, I'd like the text to have 5px padding on either side under 570px screen width.

Instead, the text width decreases significantly as the screen collapses.

I'm guessing it has to do with the Bootstrap 12-column division, so how'd I include the code that says to use 12 columns when the screen size is less than 570px?

Also, I've used the following link to get the paragraph/text to be the initial width I want it to be, but when it comes to decreasing the screen width, the text collapses into a narrow width.